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Old 01-15-2009, 04:54 PM   #1
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Traffic Tactics: Left-Turning Vehicles

Most crashes between a motorcycle and a left-turning vehicle are preventable. And many can be prevented easily by maintaining speed consistent with the traffic environment.




How fast does a motorcycle have to be going to do this kind of damage? We'll probably never know. I doubt that crash investigators' momentum equations can account for a car being knocked on its side, then spun around 180 degrees while sliding. So "real frickin fast" is as close as we'll get.

One news source said simply that the westbound motorcycle (moving away from the camera) hit the Honda Civic as the car turned from eastbound to northbound (to the right in the photo). If that's all you knew about the crash it would be pretty clear-cut, wouldn't it? Driver violated the rider's right of way. But the photo--from another source--tells a different story. When a rider is going that fast--especially in a residential area with a 45mph speed limit--the law doesn't necessarily give him the right of way. As a CHP officer said when talking about speed in a different crash: "The motorcycle community's take on it is someone turned in front of them. But when speed is that excessive you give up your right of way. You can't expect people to judge your speed and location accurately when you're going 45 miles over the speed limit."

This thread isn't about the law, though, it's about preventing crashes. And--in my opinion--most crashes between a motorcycle and vehicle crossing its path can be prevented with basic skills and good judgment. The skills can be acquired with a basic MSF course and maintained with practice. Judgment, OTOH, may require you to think about traffic in new ways.

The Truth About Left-Turn Crashes

While a crash between a motorcycle and a left-turning car is almost always assumed to be the fault of the driver, the truth is that many (though not most) are caused by the rider. Of 159 fatal motorcycle crashes in the Bay Area in 2006-2007, 33 involved a car crossing the motorcycle's path, usually a left-turner, either oncoming or from a side street. Of those 33 crossing-vehicle crashes, 17 were caused by the driver, 14 by the rider, and 2 are undetermined. Among the 14 caused by the motorcyclist, the rider ran a red light or stop sign in 7 of them, and in the remaining 7 excessive speed was cited as the cause, with speed from 15 to 35mph over the limit reported. It's pretty obvious how running a red light can cause a crash, but the contribution of speed can be more subtle.

How Speed Contributes

At high speed a motorcycle becomes a danger that a driver must reckon with when it is still far down the road. In the worst case, the motorcycle is on a collision course even though it is out of sight, beyond an intervening bend or rise. The driver checks carefully, sees clear roadway, and begins his turn. But before he completes it, a motorcycle rounds the bend and collides with the car. Driver inattention has nothing to do with that kind of crash.

A speeding rider can also be in danger when the road is straight, level, and unobstructed because a driver has a limited decision horizon or span of road he checks before proceeding. He looks only as far as he must to make sure his maneuver won't interfere with traffic moving at the speed he expects to find on that road. It's an intuitive judgment, not a precisely measured one, but if a driver can safely cross 200 feet ahead of the normal 30-mph traffic, he won't worry about vehicles 300 feet away because he assumes they're moving at normal speed.

Even if a driver does see a motorcycle coming from farther away, he may not judge its speed correctly. When an object is moving straight toward an observer, the visual cue for speed is increasing size. Since a distant motorcycle is just a small point in the visual field to begin with, it doesn't grow noticeably in size until it is quite close. If it's far away, even an extremely fast-moving motorcycle is an inconsequential dot in the background.

A motorcycle's acceleration can be deceptive too. From a standing start, an aggressively accelerated motorcycle can cover ground in half the time it takes a car. A driver waiting to turn left might ignore vehicles stopped at a light a half-block ahead because they're too far away to be a threat. He expects a safe 10-second interval in which to turn, but he'll have only 5 seconds if one of them is a hard-charging motorcycle.

Finally, speed reduces a motorcycle's visibility to drivers because it decreases the time spent in a limited visual field, and that limits the chance of being seen. A driver preparing to turn may have to keep track of traffic coming in three different directions, so he's spending only one-third of his attention looking in any one direction. Traveling at 100 feet per second (70mph) a motorcyclist might not even be in the picture when a driver makes a quick glance toward him.

"Slow Down in Town"

When riding in an area where crossing traffic is a potential hazard, think about your speed and match it to the uncertainty of the environment:
  • Maintain speed consistent with the normal flow of traffic. When in doubt, obey the speed limit. It's often a good idea to be going slightly faster than adjacent traffic to stay out of blind spots. But if there is no adjacent traffic, that rule doesn't apply. And "slightly" doesn't mean 20mph.

  • Be able to stop in the distance you can see to be clear. When rounding a bend or cresting a hill, slow down so you can stop if you happen to find a vehicle crossing your path just out of sight.

  • Save the hard acceleration for open roads. Sometimes it's necessary to squirt ahead of a knot of vehicles to give yourself some breathing room, but accelerate only as hard as necessary to improve your position and don't exceed the prevailing flow of traffic.
In a Sport Rider magazine riding tip, Nick Ienatsch offered this excellent advice about speed, under the heading "Slow Down in Town":
Slowing down gives your brain a chance to notice things and more time to react. Your peripheral vision widens and you relax enough to read and predict traffic. Try walking down the supermarket aisle and reading labels, then try running down the same aisle. Now imagine all those soup cans are about to jump into your path and you'll see how slowing down affects your perception. There are plenty of places to go fast, but in and around traffic isn't one of them. If you can't slow down in town, put me in your will.

Excessive speed on the part of the motorcyclist contributes to one-quarter of Bay Area fatalities in crashes with crossing vehicles, and the tactics recommended here can help prevent them. Riders running red lights account for another quarter. It should be obvious how those can be prevented. But what about the other half, where drivers are at fault? They too, are preventable--most of the time, at least. Tactics for dealing with them will be the subject of another post.
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Old 01-15-2009, 04:59 PM   #2
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Awesome post - thanks DD!
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Old 01-15-2009, 06:09 PM   #3
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Also, if you know you're going faster than most traffic, when a situation arises where a possible left turner is seeing you, account for the fact that they will likely misjudge your speed, and either slow down some, or determine where you will go when they turn in front of you.

After all, once you've slowed down, you get to accelerate again, so no harm done, right?

I guess it's all part of assuming you're invisible, but we can't actually act like that's the case all the time, because in reality we are seen a lot, and people give way or yield. If we really were invisible, perhaps we'd be safer as we'd REALLY have to account for everything.

I do not ever feel safe on the bike on a road that has a high potential for left turners. It's the #1 place that I won't have enough time to react if someone makes a last minute move.

Sorry, too many words.
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Old 01-15-2009, 06:35 PM   #4
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Every left turn driver i see up ahead makes me think about this...i usually always make a swerving motion back and forth slightly to get the drivers attention with my headlight. It helps the drivers determine my distance better i gather too.
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Old 01-17-2009, 06:53 AM   #5
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I flash my headlight off and on if I think there is any chance of an "incident", and slow down as well.
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Old 01-17-2009, 07:24 AM   #6
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I shake my bike for some reason this always gets their attention and I will yield my position but use my horn
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Old 01-17-2009, 08:51 AM   #7
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The horn isn't used as often or as widely in America as it is used overseas. +1 on horn usage...

Ride a moto in london and develop quickly or painfully... It's even worse in asiatic countries I bet
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Old 01-17-2009, 08:58 PM   #8
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Motion Camouflage

As it attacks prey, a dragonfly hides itself by flying in a straight line directly toward the victim, so it looks like a stationary object in the background. The same effect can make a motorcycle go unnoticed in traffic.


Quote:
Happy Hornet wrote: I shake my bike for some reason this always gets their attention
Quote:
4tuneit1 wrote: i usually always make a swerving motion back and forth slightly to get the drivers attention with my headlight. It helps the drivers determine my distance better i gather too.
Excellent advice. An article in the UK magazine Bike suggests why that works. Oddly enough, according to their safety expert, the answer is related to how insects attack prey.

When attacking, a dragonfly stays directly in the line of sight between its potential dinner and a fixed point in the distance. If dinner moves, the dragonfly alters its path just enough to stay on that line of sight. This tactic has the effect of keeping the predator at the same point in the prey's visual field. Because the victim sees no change in the big picture, it doesn't notice the motion and is unaware of the impending attack.

This effect is called motion camouflage, and it works because motion is difficult to perceive when it is directly along the line of sight. Since the object is stationary relative to the background, an observer doesn't see a change in the overall image and thus isn't cued to the presence of a moving object.

Though an approaching object increases in apparent size as it gets closer, it grows slowly when it is far away and will go unnoticed, especially if it is small. But as it gets closer, apparent size increases more rapidly. Moving from 1000 feet away to 900 feet, little change is seen. Advancing from 200 feet to 100 feet takes the same amount of time as 100 feet of movement at the greater distance, but the increase in apparent size is much more noticeable. Eventually the object seems to grow suddenly in size, and the motion camouflage is broken. That is called the looming effect.

A motorcycle is susceptible to motion camouflage because it is just a one-dimensional point in a driver's visual field when it is far away. And, according to the Bike article, when a driver is startled by the looming effect as he suddenly becomes aware of the motorcycle, he may freeze in his tracks. That would account for stories about the oncoming left-turner who stops in the middle of an intersection, making a bad situation even worse.

Duncan MacKillop, the riding instructor who related motion camouflage to motorcycling, suggests that diverging from a direct line of sight will break the camouflage and get the driver's attention:
I observed a smooth, gentle, single, zigzag motion, at any point along the line, created a rapid edge movement against the background and destroyed the motion camouflage. Drivers' eyes snapped towards me and they froze the movement I swept left to right and back again.
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Old 01-18-2009, 06:13 AM   #9
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Great post, Dan. An observation that I've read related to the motion camouflage topic is that due to a motorcycle being narrow and having only a single headlight, or two closely grouped headlights, makes it very difficult to judge its approach speed. As you state, the relative size of the motorcycle does not change much in a driver's visual field until they are quite close. Compare that to a much wider car and it is easy to understand one more way in which drivers can underestimate our closing speed.

I also use the wiggle/weave technique when I want to increase my visibility (as well as that hi-viz yellow jacket). I'm not so certain about flashing my headlight, as it seems that signal can be misunderstood. Last winter one of our BARF regulars had an experience in which he slowed and flashed his headlight at a car coming out of a driveway. The driver took that signal to mean, "please proceed". A collision resulted.

The point of the story is not whether flashing your headlight is effective at making yourself visible or not. The point is that even when you weave, wear hi-viz yellow, ride with your HID lights one, etc., that drivers may still violate your right-of-way. When that happens, you as a rider you must leave yourself a margin in speed, space, skill and judgment that will enable you to react effectively and avoid the imminent collision.
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Old 01-18-2009, 08:16 AM   #10
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Dan, this is one of your best yet.
Very good information, even if left turning cars are involved in only 20% of all fatal crashes.
Your point about reaching the crest of a rise is very valuable, and for many more reasons than just the possibility of a car turning left where the driver can't see you.
On unfamiliar backroads, you have no idea what the road is going to do on the other side of the rise, and I know of a number of crashes that occurred because of a turn or road hazard just the other side of the crest.
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Old 01-18-2009, 08:43 AM   #11
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Quote:
Originally Posted by afm199 View Post
I flash my headlight off and on if I think there is any chance of an "incident", and slow down as well.
This is what I wrote about the same thing in the Crashproof thread:

I never use "flashing" on my bike as a "warning."

Often people take it to mean "go ahead" like when you're on a freeway, the big rig wants to pull into the fast lane to go around a slower truck, but traffice is dense. Being courteous, you drift back to give the rig space, "flash" your lights and he (or she) takes that as a "yes, it's ok to move over."

Usually when the truck has completed its pass it will double blink its emergency flashers as a "thank you."

At least that has been my experience and is why I only flash my lights as an "OK" rather than as a warning.

If someone is in the fast lane but going below the limit on the freeway, and blocking the lane, I don't even flash my lights then.

Too many road ragers out there.


And as some of you may know, as I've related it several times, I was "left turned" in March of '07 after 36 years of success at evasion. It is a crash I've run over in my head countless times and I believe my mistake was looking to make eye contact as I wasn't even sure there was anyone in the car as it had sat there apparently waiting to make a left in front of me (no turn signal on). The car sat for the 20 seconds it took to approach from several blocks away with no other traffic around on a bright sunny Sunday afternoon in Downtown Santa Rosa.

I had done the whole swerving thing, slowed my pace, but I started to convince myself the car must be empty and stalled in the intersection or something which is why I took my eyes off the front wheels to look at where the driver's face would be.

That is when I saw the big granny glasses and the 85 year old granny pulled in front of me. I swerved to aim for the rear of the car, the bike and I went down, the bike punched a hole in her right rear door and I rolled behind her relatively unscathed as there was no other traffic to run me over.

She told the cops and the insurance adjusters that she had, indeed, seen me, but that SHE had a green light and therefore felt she could make that left any old time she pleased. Why she waited with no other traffic at all, I really have no idea.

Supposedly they took away her license...but I'm not so sure.

Still miss that K75S that Chris at San Jose BMW had waved his magic wand over; the engine work they did transformed that rather bland powerplant and I enjoyed it for 20 years.

Sure, the F800ST I replaced it with is a better bike in many ways, but I loved that bike and planned never to sell it.

Sigh.
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Old 01-18-2009, 10:42 AM   #12
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I actually got pulled over for doing the motion swerve by a Fresno LEO... I explained why i swerve (not a violent swerve). He agreed, and just wanted to see if I was drunk though..lol

Also to add to the manuever... From the drivers perspective it is something that is out of the norm. So what it triggers in the cager is a pause-response that might prevent them from immediately putting their vehicle in the way of another vehicle that is acting somewhat erratic. The driver thinks something is not normal, and usually won't want to continue in their left turn until the threat is passed.

Last edited by 4tuneit1; 01-18-2009 at 10:45 AM..
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Old 01-19-2009, 03:23 PM   #13
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Originally Posted by 4tuneit1 View Post
I actually got pulled over for doing the motion swerve by a Fresno LEO... I explained why i swerve (not a violent swerve). He agreed, and just wanted to see if I was drunk though..lol
I use that technique as well. I already planned my explanation for it, in case I'm pulled over...

"I use this maneuver to make sure I'm noticed. You noticed me, didn't you?"
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Old 01-20-2009, 07:52 PM   #14
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Re. flashing lights

When I approach an "iffy" situation I will hold down my light switch which will illuminate both of my Buell's headlights, one on low and one on high. I also wiggle the bars, cover the horn button and watch the cars left front tire.
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Old 01-21-2009, 03:26 PM   #15
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After getting left-turned as a noob, I use the "bee dance" swerve when I'm approaching an intersection with potential left-turners, too. It seems to break up the dragonfly effect quite well--I often see the eyes of the other driver snap to attention when I do it.

Other than getting pulled over by overzealous LEOs for this behavior, can anyone think of a reason that it might not be a good idea? I have a certain amount of concern that if someone were to turn in my path anyway while I was in the midst of the back-and-forth, I might not be able to react as quickly.
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